WHITE-PINE BLISTER RUST. 35 
fected area. They must have been produced by aeciospores which 
had been blown at least the above distances. 
In 1919, York caught and germinated aeciospores on the summits 
of two mountains nearly 4,300 feet above the adjoining lowlands. 
It is evident that altitudes such as this do not prevent the spread 
of this fungus. Pennington 18 caught aeciospores up to 1,200 feet 
distant from pines and found diseased Ribes three-fourths of a mile 
from any pine tree. 
AGENTS DISSEMINATING THE ^JCIOSPORES. 
It has been evident from the beginning that wind is a most efficient 
and active agent in the distribution of the spores of Cronartium 
ribicola. While the probability of spore carriage by other agents 
such as insects and the larger animals was recognized, no time could 
be spared for work upon it. More recently, Gravatt and Marshall 
(45) and Gravatt and Posey (46) have made some studies of this 
sort. 
Gravatt and Marshall worked in the experimental greenhouse 
where no aecia were present. They found that pycnia and the 
surrounding bark tissues were eaten by sow bugs. 
Gravatt and Posey (46) made studies in the field in a heavily 
infected pine area at K'ittery Point, Me. Here it was found that 
gipsy-moth larvae, which were abundant, fed eagerly on the 
pycnia and secia of the blister rust and also ate the bark tissues 
immediately adjacent to them. It was found that in some cankers 
a considerable percentage of the fruiting aecia were thus destroyed. 
But a few ingested spores remained viable, as tests in hanging drop 
cells in tap water yielded a few germinations. These larvae also 
were carriers of abundant aeciospores on their bodies, many being of a 
decided yellow color from the spores with which they were dusted. 
The gipsy-moth larvae are known to have been blown 20 miles or 
more. Within the gipsy-moth infested area these larvae are then 
dangerous agents in the distant spread of the disease, a fact not 
previously appreciated. 
Notes made by Gravatt show that a wood mouse caught in the out- 
break area at Kittery Point, Me., carried a small number of aeciospores 
on its body. WTiile squirrels, other animals, and birds have not been 
examined, there can be no doubt that they are active carriers of the 
spores. It is known that the aeciospores become attached readily 
to clothing, and there can be no doubt that persons may carry the 
disease, at least locally, in this manner. 
In a number of outbreak areas where pine infections were just about 
to produce pycnia for the first time, it was noted by several observers 19 
is Pennington, L. H. Op. cit. 
w Rhoads, A. S. Op. cit. 
